As background, the distinction between a film and a coating is very loosely defined and is not important to the operation or description of the present invention. In one definition, a film would be considered as a layer under about 10 .mu.m thick, and a coating would be of greater thickness. In the present description, however, the terms are generally used interchangeably.
The following are examples of previously proposed techniques for generating such films, coatings and powders: physical vapour deposition (PVD) (a generic term given to a variety of sputtering techniques such as radio frequency (RF) sputtering, reactive magnetron sputtering and ion beam sputtering); flame spray deposition (FSD); the so-called sol-gel process; electrostatic spray pyrolysis (ESP); and chemical vapour deposition (CVD). Two particular examples are disclosed in EP-A-0 103 505 and Applied Physics Letters, Vol. 67, No. 22, November 1995, pp 3337-3339.
However, none of these techniques has been found to provide good control of the stoichiometry, morphology, microstructure and properties of multicomponent oxide films and a relatively high growth rate and deposited area of a deposited film. Also, the CVD and PVD techniques tend to need expensive equipment and highly skilled technicians for effective operation.